The shapes of the illuminated surface of the moon as seen from the earth. The shape changes as a result of the relative positions of the earth, sun, and moon.

New moon occurs when the nearside is totally unilluminated by the sun. As the moon moves eastwards in its orbit the sunrise terminator crosses the nearside from east to west producing a crescent moon. The moon is half illuminated at first quarter. When it is more than half-phase but less than full phase it is said to be a gibbous moon. When the moon is at opposition the nearside is fully illuminated producing a full moon. The sunset terminator then follows to produce a waning gibbous moon, last quarter, a waning crescent moon, and eventually the next new moon.